This invention relates generally to endoluminal stents, grafts, and/or prostheses and, more specifically, to braided implantable devices adapted for deployment in branched lumina and processes for their manufacture.
A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called xe2x80x9cminimally invasive techniquesxe2x80x9d in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or xe2x80x9cintroducerxe2x80x9d to the site where it is required. The introducer may enter the body through the patient""s skin, or by a xe2x80x9ccut downxe2x80x9d technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these wire stent configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference, the ""771 Wallsten patent being only one example of many variations of braided stents known in the art and thus not intended as a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. The flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where the lumen of the vessel often becomes contorted and irregular both before and after placement of the stent.
Braided grafts are also known in the art. U.S. Pat. Nos. 5,718,159, 5,758,562, and 6,019,786 to Thompson and 5,957,974 to Thompson et al. (hereinafter xe2x80x9cthe Thompson patentsxe2x80x9d) and incorporated herein by reference, describe braided graft structures, composite braided stent/graft structures having wire stent filaments interwoven with fabric graft yarns, and processes for their manufacture. In addition to the circular braiding processes described in the Thompson patents, other braiding technologies are known in the art, although not typically associated with the fabrication of implantable medical devices. For example, U.S. Pat. No. 4,881,444, to Konrad Krauland, U.S. Pat. No. 4,885,973 to Raymond Spain, and U.S. Pat. No. 4,621,560 to Brown et al. generally describe 3-dimensional braiding equipment and processes, also referred to as Cartesian braiding or jacquard braiding. Such braiding technology is typically used to make fiber-reinforced structural members, where, for example, fibrous structures are braided and then coated with a resin that hardens, providing a structure wherein the fibers provide tensile strength and the hardened resin provides compressive strength.
Among the many applications for stent-grafts is for deployment in bifurcated lumen, such as for repair of abdominal aortic aneurysms (AAA). Various stent-graft configurations are known in the art for bifurcated applications, including single-piece and modular designs, graft designs fully supported by stents, and graft designs only partially supported by stents. Referring now to FIGS. 1A and 1B, there are shown the components of a modular, non-braided, bifurcated, stent 10 for use with a fully-supported graft as is fully described in U.S. Pat. No. 5,609,627 to Goicoechea et al and adapted for implantation within the aorta of a human. By xe2x80x9cfully-supportedxe2x80x9d it is meant that the graft is adapted to have stent structure underlying the graft throughout the entire length of the graft, as opposed to having extensive lengths of unsupported graft between anchoring stent portions, as will be described herein later.
As shown in FIG. 1A, stent 10 comprises a main body 12 which bifurcates into a first frustoconical leg transition 14 with a dependent first leg 16, and a second frustoconical leg transition 18. Second leg 20 is a modular component comprising a frustoconical part 22 adapted to interlock within second leg transition 18, and a depending portion 24. Frustoconical part 22 may have barbs 23 to help firmly connect second leg 20 to leg transition 18. As shown in FIG. 2, such a bifurcated stent 10 is typically implanted within the vasculature such that the main body 12 and leg transitions 14 and 18 are positioned within the aorta main portion 26 and with the dependent first leg 16 and depending portion 24 of second leg 20 each positioned within respective iliac arteries 28 and 30. Modular designs are also available wherein both legs are modular components. All of the bifurcated stents described herein, regardless of underlying structure, generally resemble the configuration shown in FIG. 2 when fully implanted.
As shown in FIGS. 1A and 1B and as fully described in the ""627 patent, the structure of stent 10 is a continuous wire zig-zag structure comprising a series of struts 32 joined at apices 34 and wound into hoops 36, with abutting hoops joined together in some manner, such as with sutures, at abutting apices. One potential disadvantage of zig-zag stent architecture is that the apices of the zig-zag structure can rub against the graft, causing wear in the graft.
Modular, fully-supported, bifurcated stent-graft designs using braided architecture are also known. Such designs typically comprise a tubular stent and/or graft that is crimped or pinched together in the middle or at one end to form a septum and two smaller lumina. These two lumina can then be used as sockets for the iliac sections. The braided stents have the advantage of being very adaptable to tortuous anatomy as compared to other stent architectures. The formation of the crimp, however, can cause metal cold-work and embrittlement in the stent wires and can result in bulkiness in the bifurcation region, requiring a relatively larger deployment profile than other designs.
To overcome the potential disadvantages of modular designs, it is also known to provide one-piece or xe2x80x9cunitaryxe2x80x9d stent designs. Such known designs may be fully supported or only partially supported, such as by having anchoring stent portions only located at the end sections adjacent each opening of the graft. One piece stent designs having a zig-zag stent architecture still have the same disadvantage of potential graft wear due to rubbing of the apices. One-piece graft designs that are only partially supported have the potential disadvantage that the differences in radial strength and flexibility between the unsupported and supported regions make the stent-grafts susceptible to kinking when navigating through tortuous lumina.
The invention comprises a branching implantable device for deployment in a lumen. The device comprises a body that branches into a plurality of legs, wherein at least a first leg portion of each leg comprises a discrete plurality of continuous strands braided together and at least a first body portion of the body comprises at least one of said continuous strands from each discrete plurality of continuous strands braided together. The device may comprise a stent, a graft comprising a plurality of fabric yarns, or a composite stent-graft comprising a plurality of fabric yarns interbraided with a plurality of structural stent filaments.
The invention also comprises a method for treating a diseased branched lumen, the branched lumen comprising a main section that branches into a plurality of branches. The method comprises the step of deploying within the branched lumen a branching implantable device comprising a body that branches into a plurality of legs. At least a first leg portion of each leg comprises a discrete plurality of continuous strands braided together. At least a first body portion of the body comprises at least one of said continuous strands from each discrete plurality of continuous strands braided together. The deployment step comprises deploying the body in the main section and deploying each leg within one of the branches.
The invention further comprises a process for constructing a braided, branched implantable device having a body and a plurality of legs, each leg comprising a discrete plurality of strands. The process comprises the steps of braiding a first plurality of continuous strands to individually form at least a portion of a first leg; braiding at least a second plurality of continuous strands to individually form at least a portion of a second leg; and braiding at least one strand from each of the first plurality of continuous strands and the second plurality of continuous strands together to form at least a portion of the body. The legs may be formed sequentially before the body, or vice versa. The steps may be performed using circular braiding equipment, in which case the first leg may be formed sequentially before the second leg. The steps may also be performed using cartesian braiding equipment, in which case the legs may be formed simultaneously.
The invention also comprises a process for constructing a braided, branched, implantable, tubular device having a body and a plurality of legs, where the process comprises the step of first creating a plurality of flat-braided strips having longitudinal edges. The, at least one portion of one longitudinal edge of one strip is attached to a corresponding portion of an opposite longitudinal edge of another strip. This step is repeated to attach selected portions of the longitudinal edges of the plurality of strips to one another until the braided, branched, implantable, tubular device is formed.